1. Field of the Invention
This invention relates to an input circuit for portable electronic device and more particularly to an input circuit for a portable electronic device which functions also as a stop watch capable of measuring an extremely short time of at least 1/100 second.
2. Description of the Prior Art
Heretofore, it has been the common practice to use an input circuit shown in FIG. 1 as an input circuit for portable electronic devices such as an electronic timepiece. In such prior art input circuit shown in FIG. 1, provision is made of a flip-flop 2 for the purpose of removing chattering pulses induced in an operating signal delivered from an exteriorly operable member 4. If the flip-flop 2 is supplied with a reading in signal .phi..sub.32 having a frequency of 32 Hz, it is possible to remove chattering pulses within 30 m.sec. Such conventional input circuit, however, has involved a delay of at most 30 m.sec. from the operation of the exteriorly operable member 4 to appearance of the operating signal on an output line of the flip-flop 2. If such conventional input circuit is used for an electronic stop watch capable of measuring an extremely short time up to 1/100 second figure, a measurement error of about 0.03 second is produced. In order to prevent such measurement error, it is necessary to increase the frequency of the reading in signal .phi. for the flip-flop 2 to at least 200 Hz. For this purpose, the period of chattering pulses induced in the operating signal produced by the exteriorly operable member 4 must be reduced to at most 5 m.sec. Provision of such exteriorly operable member 4 is extremely difficult in practice.